Between 16.31 and 17.06 hours on 4 July 1944, U-539 fired torpedoes at a tanker convoy and reported four tankers with 26,000 grt torpedoed. According to the xB-Dienst one of these tankers was the American Hollywood (5498 grt). However, the only ship hit was the unescorted Kittanning, which was torpedoed three times about 40 miles northeast of Cristobal.

The Kittanning (Master Raymond J.S. Chambers) had left port at 13.30 hours, but soon thereafter the third assistant engineer fell and seriously injured himself and the master decided to return to Cristobal. At 16.31 hours, just after the ship changed course back at 14.5 knots, a torpedo struck on the starboard side at the #6 tank. At 16.46 hours, a second torpedo hit the #7 tank on the same side abaft the midships house and the ship swung hard right. The explosions opened a hole 65 feet long and 20 feet high and flooded five tanks, causing a 35° list to starboard. At 17.00 hours, the ten officers, 39 crewmen and 25 armed guards (the ship was armed with one 5in, one 3in and eight 20mm guns) abandoned ship in four lifeboats, but two boats swamped in the choppy seas and squally weather. A coup de grâce, fired at 17.06 hours, struck on the port side at the #4 tank under the midship house, causing the tanker to right herself and float on an even keel. The U-boat had reported another torpedo fired at 18.49 hours, but it seems that it had missed.

USCGC Marion (WPC 145) and USCGC Crawford (WPC 134) arrived, the former picked up the survivors and took them to Cristobal. The master and five men reboarded the Kittanning and USCGC Crawford began towing the tanker, but when the tow line parted, the operations halted for the night. The next morning, the tug USS Woodcock (ATO 145) arrived and took the tanker in tow. However the tug suffered engine trouble and had to drop the tow. Later the Panama canal tug Tavernilla took the ship in tow, later helped by the Panama canal tug Cardenas. With the help of the American tug Jupiter Inlet the tanker moored at Cristobal on 6 July. The Kittanning was drydocked at Balboa, before being towed to Galveston for permanent repairs.